56 Idaho Asphalt Conference October 27 2016€¦ · 56th Idaho Asphalt Conference. October 27. th. 2016. ... binder that we analyzed in 2011 where T 283 showed a TSR ... accordance
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56 th Idaho Asphalt Conference October 27 th 2016 Performance Graded (PG) Asphalt Binder Modification - Lessons Learned With the Hamburg and MSCR Joe DeVol Assistant State Materials Engineer State Materials Laboratory
But first I’d like to share a few facts about our agency that you might find of interest. Last year we finally passed a transportation bill.
Washington StateDepartment of Transportation
• Just the Facts
– WSDOT manages 18,500 lane miles
– Smooth, safe and economical pavements
– 2016 forecast
• 1,043,000 tons HMA
• 586,555 tons HMA - modified asphalt
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A little bit about our agency.
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This is just a graphic representation of the forecast which can be found on our website, along with details like which grade of asphalt binder is used in what region of the state and the anticipated tonnage of HMA.
• Background How we got to where we are
• SHRP efforts - 1995
• Implemented PG Binders - 2000
• Superpave Volumetric Mix Design - 2004
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As a little background about how we got to where we are now. Pooled fund study.
• Hamburg & MSCR What have we learned?
• Asphalt and Anti-Strip Compatibility
• Asphalt Modification – Products and Processes
• Benefits of Polymer Modification• Note: Dual testing AASHTO M 320 & M 332 since 2008
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Now, I want to explain what we have learned in the last few years about the importance of… And how the Hamburg Wheel Track Tester, the Elastic Recovery Test and the MSCR test helped us identify deficiencies in our standard specifications. As a footnote we have been dual testing and collecting data on our asphalt binders using AASHTO M 320 and M 332 since 2008.
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We purchased our first Hamburg in 2010 and began testing all of our HMA mix designs with this device. We have two of these original PMW Hamburg Wheel Track Testers at our State Materials Lab in Tumwater.
• Hamburg Testing
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Imagine our excitement when we found this high quality HMA in 2010.
• Hamburg Testing
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Or this
• Hamburg Testing
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This is an example of a mix design with neat binder that we analyzed in 2011 where T 283 showed a TSR benefit, but little benefit realized with HWTD.
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This is a graphic representation of this mix design.
Hamburg Samples with PG64-28 “Original Formulation”
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5 1000 3500 6000 8500 11000 13500 16000 18500
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Hamburg Mix Design Verification Test Data
0% Antistrip
0.50% Antistrip
Rut D
epth
in M
illim
eter
s
Number of Wheel Passes
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So here is where it began to get interesting. This was one of our typical ½ inch HMA mix designs from 2011 with what we expect to be a modified PG64-28 binder. According to our modified lottman test we should use 1/2% anti-strip for an optimum tensile strength. But the Hamburg test tells a different story.
In review, our test data showed that the PG64-28 met AASHTO M 320 requirements. And we saw in increase in tensile strength with anti-strip, but the Hamburg results we observed would fail many agency specifications.
After analyzing the test data we contacted this particular asphalt supplier and asked about their modification process. They were very forthcoming about the products and processes they used to meet M 320. Suffice to just say it wasn’t polymer modification they were using. As an experiment we took that exact same mix design and a polymer modified version of this same suppliers PG64-28 and this was the result.
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5 1000 3500 6000 8500 11000 13500 16000 18500
Hamburg Mix Design Verification Test Data
0% Antistrip0.50% Antistrip
Rut D
epth
in M
illim
eter
s
Number of Wheel Passes
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5 1000 3500 6000 8500 11000 13500 16000 18500
Axis Title
Hamburg Mix Design Verification Test Data
0% Antistrip
0.50% Antistrip
Rut D
epth
in M
illim
eter
s
Number of Wheel PassesHamburg Samples with PG64-28 “Original Formulation”
Hamburg Samples with PG64-28 “Polymer Modified”
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Here they are stacked on top of each other. This one mix design wasn’t the only example of what we were seeing. In review of the 2010 and 2011 test data we began to see a pattern of poor Hamburg results with use of anti-strip in what we expect to be modified asphalt in Washington State. It was obvious to us that we needed to do something other than just stop using anti-strip. The Hamburg showed that some mixes would hold up under repeated loading with no anti-strip, but there’s more to it than that.
• Asphalt Binder Testing Data Analysis
Original Formulation
• Met Conventional PG Specs (AASHTO - M 320)
• Met MSCR Specs * (AASHTO - M 332)
• Elastic Recovery = 25%(AASHTO - T 301)
*Excluding Appendix X1
Polymer Modified
• Met Conventional PG Specs (AASHTO - M 320)
• Met MSCR Specs ** (AASHTO - M 332)
• Elastic Recovery = 74% (AASHTO - T 301)
**Including Appendix X1
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This is a comparison of the original formulation and the polymer modified binder from our experiment.
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Here are the results of the two binders plotted on the M 332 graph from Appendix A1.
• Asphalt Binder Testing Data Analysis
• Typical Modified PG Binders
• Met all specifications requirements (AASHTO - M 320)
• Passed MSCR (AASHTO - M 332) *
*Excluding Appendix X1 (% recovery)
• Tested elastic recovery (AASHTO - T 301)
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The binder test data showed a pretty consistent pattern with almost all of our modified asphalt binders.
• Hamburg & MSCR Where are we today?
• Elastic Recovery Specification - 2012
• Hamburg and IDT Specification - 2014
• Multiple Stress Creep Recovery - 2018
Elastic Recovery Specification
Property Test Method Additional Requirements by Performance Grade (PG) Asphalt Binders
AASHTO T 3012 -- -- 60% Min. 60% Min. 60% Min. 60% Min.
Notes:
1. Elastic Recovery @ 25°C ± 0.5°C2. Specimen conditioned in accordance with AASHTO T 240 – RTFO
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After years of discussions with our eastern side of the state regarding what they felt were dry looking, rapid aging, under asphalted mixtures - coupled with what we learned from the Hamburg and our binder test data we decided it was time to implement a PG Plus spec, AASHTO T 301. Since MSCR was not fully supported yet we opted to implement an Elastic Recovery Spec in 2012 in an effort to ensure we get binders that will provide long term field performance.
Hamburg and IDT Specification
Mix Criteria
HMA Class
⅜ inch ½ inch ¾ inch 1 inch
Min. Max. Min. Max. Min. Max. Min. Max.
Hamburg Wheel-Track Testing, WSDOT FOP for AASHTO T 324Rut Depth (mm) @ 15,000 Passes
10 10 10 10
Hamburg Wheel-Track Testing, WSDOT FOP for AASHTO T 324 Minimum Number of Passes With no Stripping Inflection Point
15,000 15,000 15,000 15,000
Indirect Tensile (IDT) Strength (psi) of Bituminous Materials WSDOT FOP for ASTM D 6931
175 175 175 175
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After the third year of collecting test data we implemented our Hamburg and IDT specification in 2014.
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This is a graphic representation of our HWTD spec. We are currently evaluating the method to mathematically determine the stripping inflection point or Stripping Number.
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This is a graphic representation of our IDT testing. We are also evaluating a way to improve or enhance the IDT we are using by measuring the area under the curve and evaluating the fracture work concept. This came from some research conducted by WSU.
• Multiple Stress Creep Recovery Where we’re headed next!
• Multiple Stress Creep Recovery - 2018* Working with PCCAS, Regional Task Group & WAPA
• Would Replace Elastic Recovery
• New PG Grading Terminology
• Current Grading System
– Base grade (Environment)
– Grade bump (Traffic/Load)
– Bump = same stiffness at higher temperature
– Allows for products & processes that may affect performance
• MSCR Grading System
– Base grade (Environment)
– Grade bump (Traffic/Load)
– Bump = increase stiffness at service temperature
– Requires products & processes that ensure performance
• Asphalt Binder Grading - 101
• Current Grading System
– PG58-22
– PG64-22
– PG70-22
– PG64-28
– PG70-28
– PG76-28
• MSCR Grading System
– PG58S-22 (Standard)
– PG58H-22 (Heavy)
– PG58V-22 (Very Heavy)
– PG64S-28
– PG64H-28
– PG64V-28
• Asphalt Binder Grading - 101
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Initially, there was a lot of discussion/concern that adoption of MSCR would create more grades of binder, but we don’t see it that way.
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This chart was a snapshot of how close our PG64-28 binder are to meeting the Jnr and % recovery specs of M 332.
